1. Field of the Invention
This invention relates to a new process for the production of isocyanurate polyisocyanates (polyisocyanates containing isocyanurate groups) containing urethane and ester groups, to the compounds obtained by this process and to their use as the polyisocyanate component for the production of polyurethane plastics, in particular two-component polyurethane lacquers (coatings).
2. Description of the Prior Art
The production of isocyanurate polyisocyanates is known (cf. for example GB-P 920,080, DE-AS 1,667,309, DE-OS 3,100,262, DE-OS 3,219,608, DE-OS 3,240,613, EP-A-10,589, EP-A-57,653, EP-A-89,297 or EP-A-187,105). Some of these prior publications also mention the use of subequivalent quantities of compounds containing hydroxyl groups. Thus, DE-AS 1,667,309 for example describes the production of isocyanurate polyisocyanates using compounds containing hydroxyl groups as co-catalysts. DE-OS 3,219,608 describes a use of polyhydric alcohols having a molecular weight below 3000 in a quantity of up to 15 mole-%, based on HDI used, in the production of isocyanurate polyisocyanates based on this starting diisocyanate. Suitable polyhydric alcohols according to this prior publication also include unspecified polyester polyols. In the process according to EP-A-155,559, low molecular weight diols containing lateral alkyl groups are used as modifying agents.
In all the known prior-published processes, the object of the urethane modification is merely to provide a suitable solvent for the catalyst, to achieve suitable co-catalysis or to establish compatibility with various polyols. None of the prior publications cited above discloses how it is possible to modify isocyanurate polyisocyanates in such a way that they are optimally suitable for the production of highly elastic lacquers which retain their elasticity, even at low temperatures of down to -40.degree. C.
Aliphatic isocyanurate polyisocyanates, particularly those based on 1,6-diisocyantohexane (hereinafter referred to as "HDI"), have acquired industrial significance. They are primarily used as the polyisocyanate component in two-component polyurethane lacquers, but may also be used for the production of moisture-hardening one-component polyurethane binders or, when blocked by blocking agents for isocyanate groups, in heat-crosslinkable polyurethane lacquers. These lacquers are used mainly for lacquering non-flexible substrates, such as metal and wood, and are distinguished by high light stability and weather resistance, extreme hardness and very good adhesion. HDI-based isocyanurate polyisocyanates are particularly distinguished from corresponding biuret polyisocyanates, which are also used on an industrial scale, by greatly improved resistance to yellowing and chemicals, for example by their resistance to tar stains.
The chemical bases for the various polyurethane lacquers are described inter alia in "Lackkunstharze" by Hans Wagner and Hans Friedrich Sarx, Carl Hanser Verlag, Munchen 1971, pages 153 to 173 and in "Lehrbuch der Lacke and Beschichtungen" Vol. 1, Part 2, by Hans Knittel, Verlag W. A. Colomb, Berlin-Oberschwandorf 1973, pages 512 to 612.
However, state-of-the-art polyurethane lacquers, particularly two-component polyurethane lacquers, often lead to highly crosslinked lacquer coatings wherein the elasticity often fails to satisfy the requirements of coatings for flexible substrates. Flexible plastic components are being used to an increasing extent, particularly in the automotive field, in efforts to improve safety. These flexible moldings (fenders, spoilers, wing mirror housings and the like) are relatively large and, accordingly, largely determine the external appearance of the vehicle. For this reason, moldings of the type in question have to be lacquered. In addition, the surfaces of the plastics are degraded by the effects of weather and hence have to be protected accordingly.
However, elastic lacquer films are also required for non-elastic plastic moldings to prevent mechanical damage to such moldings. For example, hard, but tough thermoplasts have to be lacquered with highly elastic, extremely resistant lacquers to prevent the lacquer film from cracking in the event of mechanical damage or under the effect of other external influences and the cracks from propagating in the compact plastic. Accordingly, the lacquer finish, above all the surface lacquer, applied to such moldings has to satisfy demands far exceeding those of a normal lacquer finish.
These problems were partially solved by the development of hydroxyl polyesters and polyacrylates which, by virtue of their structure, can be processed to elastic lacquer films. However, it was not possible in this way to eliminate all existing difficulties. The lacquer films formed are often not sufficiently hard and are not sufficiently crosslinked and/or resistant to chemicals.
In addition, the diisocyanate-based, for example HDI-based, isocyanurate polyisocyanates available for the crosslinking of these polyhydroxyl compounds are often incompatible with the polyhydroxyl compounds or lead to clouding on dilution with various solvents.
These disadvantages have prevented known HDI-based isocyanurate polyisocyanates from acquiring any real significance in the lacquering of plastics despite their outstanding technical properties.
Accordingly, an object of the present invention is to provide new isocyanurate polyisocyanates which 1) in combination with state-of-the-art polyhydroxyl compounds provide two-component polyurethane lacquers which satisfy the particular requirements mentioned above 2) in particular, are optimally suited to the lacquering of elastic plastic moldings and 3) may also be used with advantage for the production of moisture-hardening one-component binders or, in blocked form, for the production of heat-crosslinkable lacquer binders.
This object may be achieved by isocyanurate polyisocyanates according to the invention which are described in detail in the following.